Rutager and Bert,
Sounds like you two are getting very close.....I've used different temp sensors over the years, but you both should have VDO temp sensors that get mounted in the left side chain cover (installed in the Thermo-Time sensor port) VDO does not make it easy to find the cal info....but here you go. However, the sensor tolerances are pretty wide, so calibrating, based on your Porsche gauge and/or per the patented Rutager method is advised.
regards,
AL
Rutager,
I'd be interested in see your temp sensor cal, after you verified it against a thermometer, etc. and that will be a good check against the VDO document.